The present invention relates to a metal substrate for a thin film magnetic storage disc and to a process for producing such a substrate. The metal substrate may comprise a disc composed of metal or at least one metal layer carried on a glass disc, and in this specification the term "metal substrate" is intended to cover both of those constructions.
Thin film magnetic discs for storing data are known in which a magnetic recording medium has been deposited onto a metal substrate in the form of a disc. Known metal substrates are made of aluminium or anodised titanium. In use, the magnetic disc is disposed in a magnetic disc drive unit which utilises a magnetic head for reading and writing information from and onto the disc. Prior to the reading and writing operation, the disc is stationary and the head is in contact with the magnetic recording medium on the disc. In the reading and writing operation, the disc is driven to rotate at a predetermined speed relative to the head which can be moved radially relative to the disc. The head is spaced a very small distance from the magnetic recording medium and is adapted to read information from and write information onto the magnetic recording medium at the desired place on the magnetic recording medium. After the reading and writing operation, the rotation of the disc is terminated and the head is permitted to return to the initial configuration wherein the head contacts the disc. This method of operating a disc is known in the art as a contact-start-stop (CSS) method. It is known that such magnetic disc drive units suffer from the problem of "stiction" or static friction which exists between the head and the magnetic recording medium on initiation or termination of the reading or writing operation. This stiction can cause wear of the head and of the medium and thus can reduce the life time of the magnetic disc drive unit. The tendency for stiction to occur increases with increasing smoothness of the magnetic recording medium. The metal sustrate can have such a smooth surface that the overlying magnetic recording medium which has a correspondingly smooth surface is so smooth that the surface area of the medium actually contacting the static recording head is sufficiently large whereby the stiction problem can be encountered during use of the drive unit. This can cause premature failure of the drive unit and/or the media as described above.
It is known to texture the surface of the metal substrate by mechanically abrading the surface after an initial polishing step. The abrasion is carried out either by an abrasive tape or by loose abrasive material. However, we have found that the use of mechanical abrading of the disc surface has the disadvantage that a fully isotropic micro-textured surface can be difficult to achieve.